Traditionally, there have been investigated color image recording techniques for obtaining color hard copies by means of ink jets, electrophotography, thermal transfer, silver halide light-sensitive materials, etc. Of these means, thermal transfer recording materials in particular are advantageous that they permit easy operation and maintenance and system size reduction and cost reduction and that running cost is low.
Meantime, dyes used in the thermal transfer recording material are important in thermal transfer recording; conventional dyes used for this purpose are faulty that the obtained image is poor in stability, particularly fixability and light fastness.
In an attempt to solve this problem, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 78893/1984, 109349/1984 and 2398/1985 disclose image forming methods wherein an image is formed with a chelatable thermally diffusible dye chelated on an image-receiving material.
However, although these image forming methods are excellent as to improvement of fixability and light fastness, the dyes disclosed in these patent publications do not always meet the following performance requirements for chelatable dyes used in the thermal transfer recording material (hereinafter referred to as post-chelating dyes).
1) Chelating offers a chelate dye image with good tone. 2) The post-chelating dye has good thermal diffusibility. 3) The post-chelating dye does not migrate to the ink sheet's back face etc. during ink sheet storage. 4) The post-chelating dye has good solvent solubility (ink formability). 5) The post-chelating dye has good reactivity with metal ion donor compounds. 6) The chelate dye image has excellent stability (fixability, light fastness).
There is therefore a need for further improvement in the above performance of post-chelating dyes.